Some new designs of mobile communication devices—such as smart phones, tablet computers, and laptop computers—include two or more Subscriber Identity Module (“SIM”) cards that provide users with access to multiple separate mobile telephony networks. Examples of mobile telephony networks include GSM, TD-SCDMA, CDMA2000, LTE, and WCDMA. Example multi-SIM mobile communication devices include mobile phones, laptop computers, smart phones, and other mobile communication devices that are configured to connect to multiple mobile telephony networks. A mobile communication device that includes a plurality of SIMs and connects to two or more separate mobile telephony networks using two or more separate radio-frequency (“RF”) transceivers is termed a “multi-SIM-multi-active” or “MSMA” communication device. An example MSMA communication device is a “dual-SIM-dual-active” or “DSDA” communication device, which includes two SIM cards/subscriptions associated with two mobile telephony networks.
Because a multi-SIM-multi-active communication device has a plurality of separate RF communication circuits or “RF resources,” each subscription on the multi-SIM-multi-active communication device may use its associated RF resource to communicate with its mobile network at any time. However, in certain band-channel combinations of operation, the simultaneous use of the RF resources may cause one or more RF resources to desensitize or interfere with the ability of the other RF resources to operate normally because of the proximity of the antennas of the RF chains included in the multi-SIM-multi-active communication device.
To address the issues presented by desensitization or interference, in current DSDA devices if there is a co-existence or transmit (Tx)-receive (Rx)/Tx-Tx conflict when one subscription is performing data transfer and the other subscription is in a voice call or performing any signaling procedures, the subscription doing data transfer is assigned lower priority and its transmissions will be blanked (i.e., Tx blanking) to prevent performance degradation of the other subscription. However, Tx blanking often leads to data stalls/timeouts and abnormal temporary block flow (TBF) releases for the blanked subscription.
The problem arises because the network stops assigning Uplink State Flags (USFs) if the network does not receive any data blocks from the DSDA device for a certain duration as described in 3rd Generation Partnership Project (3GPP) Technical Specification (TS) 44.060. Thus, when Packet Data Traffic Channel (PDTCH) transmissions are not transmitted for the data transferring subscription due to the higher priority activity of the other subscription for longer than the specified duration, the network stops scheduling Radio Link Control (RLC)/Medium Access Control (MAC) blocks from the DSDA device for the assigned USF. In many networks, a counter is incremented to track whether the certain duration has been exceeded. When data is received for a USF, the counter is reset. For most networks, the value of the counter is slightly more than 8 (resulting in a certain duration of 400 ms).